Implement devlog entry delete <id>

[gustmrg]

Add support for deleting an existing entry via devlog entry delete <id>.

Context:

• README.md documents devlog entry delete <id>
• The entry command currently does not expose a delete subcommand
• Entries are stored in date-based JSON files under ~/.devlog/entries/

Expected behavior:

• Find an entry by its ID
• Show the entry being targeted for deletion
• Ask for confirmation before deleting
• Remove the entry from the correct daily log file
• Save the updated daily log back to disk

Implementation notes:

• Entry lookup will likely require scanning daily log files to find the matching id
• If the entry is the last item in a daily log, decide whether to keep an empty file or remove it
• Return a clear error when the ID is not found
• Avoid destructive behavior without explicit confirmation

Acceptance criteria:

• devlog entry delete <id> exists and appears in help output
• The command prompts for confirmation before deletion
• Confirmed deletions remove the correct entry from storage
• Missing IDs produce a clear, user-friendly error
• The resulting daily log file remains valid after deletion